Migration Evaluation

Evaluate and verify data migration before migrating your database to a cloud platform.

Based on the status of the data to be migrated and the future service scale, evaluate migration scenarios separately and make the required preparations.

**Table 1** Evaluation and preparation before data migration
Item	Description
Amount of the data to be migrated and class of the required DDM instance and RDS for MySQL instance	Use vertical sharding and then horizontal sharding to shard the source RDS for MySQL instance. Execute the following SQL statement to evaluate storage space occupied by the source RDS for MySQL instance: select concat(round(sum(DATA_LENGTH/1024/1024),2),'MB')as data from information_schema.TABLES; Partition a table with more than 10 million rows (or expected to exceed 10 million rows). Ensure that data stored on a single RDS instance does not exceed 500 GB.
Information about schemas and logical tables mapped to each table in the source database	Specify the information about logical tables mapped to each source table, including the number of data records, logical table type, schema, DDM instance, and associated RDS instances. If there is an RDS for MySQL instance available in the destination DDM instance and the target schema is unsharded, associate the RDS instance with the schema with no need to migrate table structures and data.
Compatibility	Check whether the source database uses the same MySQL version as the target MySQL instance associated with the destination DDM instance. The class and storage space of the destination instance cannot be less than those of the source database. Check whether the table structure and character set of the source database are the same as those of the destination instance. For a logical table that uses hash sharding, ensure that the number of data records to be migrated each time does not exceed 10 million. For a logical table using range sharding, the number cannot exceed 5 million. If a table contains a huge number of data records, import and export the data in batches. Specify the WHERE condition on mysqldump to limit the number of data records to be imported or exported at a time. SQL text files imported into DDM can only contain standard DML INSERT statements. Evaluate the compatibility of SQL statements in your application with DDM.

Before migrating data, collect the required information listed in Table 2.

**Table 2** Information to be collected
Source/Destination	Information Item
Source RDS instance	Connection address
	Listening port
	Database account
	Database name
	Table name
Destination DDM instance	Connection address
	Listening port
	Username
	Name of a shard on the RDS instance associated with the DDM instance
	Connection address of the new RDS instance
	Listening port of the new RDS instance
	Administrator of the new RDS instance
	Database name
ECS	EIP
ECS	Login credentials (username and password)